Light-emitting device

ABSTRACT

A light-emitting device includes a substrate; at least one light-emitting element on or above the substrate; a plate-shaped light-transmissive member having a lower surface that faces an upper surface of the at least one light-emitting element; a covering member that covers a lateral surface of the at least one light-emitting element and a lateral surface of the light-transmissive member; and a light-guiding member that is disposed between the light-emitting element and the light-transmissive member. In a plan view, a first lateral side of an upper surface of the light-transmissive member is outside a first lateral side of the upper surface of the at least one light-emitting element, and a second lateral side of the upper surface of the light-transmissive member is inside a second lateral side of the upper surface of the at least one light-emitting element.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a continuation of U.S. patent applicationSer. No. 16/939,937, filed on Jul. 27, 2020, which is a continuation ofU.S. patent application Ser. No. 16/143,363, filed on Sep. 26, 2018, nowU.S. Pat. No. 10,770,630, which claims priority to Japanese PatentApplication No. 2017-191476, filed on Sep. 29, 2017, the disclosures ofwhich are hereby incorporated by reference in their entireties.

BACKGROUND

The present disclosure relates to a light-emitting device, and moreparticularly, to a light-emitting device for a headlight.

Semiconductor light-emitting elements, such as light-emitting diodes andlaser diodes, have been brought into use as various light sources, andin recent years particularly, as light sources for vehicle headlights.These light sources for vehicle headlights are required to show, forexample, a specific light distribution called a Lambertian lightdistribution, in addition to high luminance. As a light-emitting devicesuitable for a headlight, Japanese Patent Publication No. 2015-76455discloses a light-emitting device that includes semiconductorlight-emitting elements disposed on or above the surface of a substrate,a light-reflective frame enclosing the semiconductor light-emittingelements on or above the substrate, and a transparent phosphor layercovering the upper and lateral surfaces of the semiconductorlight-emitting elements. This light-emitting device emits light in onedirection from the opening of the frame because light is reflected offthe inner circumferential wall surfaces of the light-reflective frame.The light-emitting device thus provides an enhanced illuminance on thefront of an automobile and is deemed to be suitable for a headlight.

Also, it is required to prevent a vehicle headlight in low beam modefrom dazzling a driver of an oncoming vehicle by cutting off light atthe upper side while ensuring illumination of the road surface. Theboundary of the light at the upper side that is cut off in low beam modeis called a cut-off line 210. It is preferable for safety reasons thatthe cut-off line 210 be clear, that is, that the upper side of thecut-off line 210 not be irradiated with light in low beam mode (FIG. 14). Accordingly, the optical system of a vehicle headlight is designedsuch that the cut-off line 210 is clear in low beam mode, and alight-emitting device used as a light source for a headlight is alsorequired to have such luminance characteristics that allow for anoptical system offering a clear cut-off line 210 can be designed.Specifically, the light-emitting device is required to have, forexample, a clear boundary between a light-emitting surface and alight-reflective frame (i.e., covering member) surrounding the peripheryof the light-emitting surface, that is, to have such characteristicsthat the luminance differs sharply between the outer and inner sides ofthe boundary as shown in FIG. 13 . To make the boundary between thelight-emitting surface and the covering member surrounding the peripheryof the light-emitting surface clear, as schematically shown in FIG. 15 ,it is effective to provide a large wavelength conversion member 207 tobe disposed on light-emitting elements 201, dispose the wavelengthconversion member 207 on the light-emitting elements 201 such that theperiphery of the wavelength conversion member 207 is located outside theperipheries of the light-emitting surfaces of the light-emittingelements 201, and dispose a covering member on the light-emittingelements 201 such that the wavelength conversion member 207 issurrounded.

However, the light-emitting surface of the light-emitting deviceinevitably becomes large if a phosphor plate (i.e., wavelengthconversion member) is disposed on or above the light-emitting elementssuch that the periphery of the phosphor plate is located outside theperipheries of the light-emitting surfaces of the light-emittingelements. Thus, there is a problem that the expanded light-emittingsurface of the light-emitting device makes the structure of the opticalsystem of a headlight large.

Accordingly, an object of certain embodiments described herein is toprovide a light-emitting device that can offer a clear cut-off lineusing a simple and small optical system when the light-emitting deviceis used as a light source for a headlight.

SUMMARY

A light-emitting device according to one embodiment of the presentinvention includes a substrate; at least one light-emitting element onor above the substrate, the at least one light-emitting element havingan upper surface serving as a light-emitting surface of the at least onelight-emitting element; a plate-shaped light-transmissive member havinga lower surface that faces the upper surface of the at least onelight-emitting element; and a covering member that covers a lateralsurface of the at least one light-emitting element and a lateral surfaceof the light-transmissive member. The upper surface of the at least onelight-emitting element has a rectangular shape so as to have a firstlateral side and a second lateral side opposite to each other, and athird lateral side and a fourth lateral side opposite to each other. Anupper surface of the light-transmissive member has a rectangular shapehaving a first lateral side and a second lateral side opposite to eachother, and a third lateral side and a fourth lateral side opposite toeach other. The light-transmissive member is disposed on or above the atleast one light-emitting element such that, in a plan view from abovethe light-emitting device, the first lateral side of the upper surfaceof the light-transmissive member is outside the first lateral side ofthe upper surface of the at least one light-emitting element, and thesecond lateral side of the upper surface of the light-transmissivemember is inside the second lateral side of the upper surface of the atleast one light-emitting element.

The light-emitting device according to certain embodiments describedherein can offer a clear cut-off line using a simple and small opticalsystem when used as a light source for a headlight.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic perspective view of a light-emitting deviceaccording to an embodiment of the present invention.

FIG. 2 is a schematic plan view of the light-emitting device accordingto the embodiment.

FIG. 3 is a schematic cross-sectional view taken along the line A-A inFIG. 2 .

FIG. 4 is a schematic cross-sectional view taken along the line B-B inFIG. 2 .

FIG. 5 is a graph showing relative luminance on the light-emittingsurface of the light-emitting device according to the embodiment.

FIG. 6 is a schematic plan view of a light-emitting device according toa first modification.

FIG. 7 is a schematic plan view of a light-emitting device according toa second modification.

FIG. 8 is a schematic cross-sectional view taken along the line C-C inFIG. 7 .

FIG. 9 is a schematic plan view of a light-emitting device according toa third modification.

FIG. 10 is a schematic plan view of a light-emitting device according toa fourth modification.

FIG. 11 is a schematic plan view of a light-emitting device according toa fifth modification.

FIG. 12 is a schematic plan view of a light-emitting device according toa sixth modification.

FIG. 13 is a graph showing relative luminance on the light-emittingsurface of a conventional light-emitting device.

FIG. 14 is a graph showing irradiation characteristics of a headlight inlow beam mode.

FIG. 15 is a schematic plan view of an illustrative conventionallight-emitting device.

DETAILED DESCRIPTION OF EMBODIMENTS

The present inventor has carried out earnest examinations to provide alight-emitting device that can offer a clear cut-off line using a simpleand small optical system when used as a light source for a headlight. Asa result, it has been found that a light-emitting device having arectangular light-emitting surface can offer a clear cut-off line usinga simple optical system when the light-emitting device is used as alight source for a headlight if the luminance differs sharply betweenthe outer and inner sides of one side of the boundary between thelight-emitting surface and a covering member surrounding the peripheryof the light-emitting surface. That is, if the luminance changes sharplyacross one side of the boundary of the rectangular light-emittingsurface, a clear cut-off line can be provided when the light-emittingdevice is used as a light source for a headlight even if the luminancechanges gradually across the other sides of the boundary. Alight-emitting device according to the present embodiment has been madeon the basis of the above findings.

The light-emitting device according to the present embodiment thatincludes a light-transmissive member mounted on or above thelight-emitting surface of at least one light-emitting element and acovering member disposed around the light-transmissive member. Thelight-transmissive member is mounted on or above the light-emittingsurface of the light-emitting element such that one side of thelight-transmissive member is located outside one side of thelight-emitting surface of the light-emitting element so that theluminance differs sharply between the outer and inner sides of theboundary between the above side of the light-transmissive member and thecovering member. At least one of the three sides other than the aboveside of the light-transmissive member is located inside one side of thelight-emitting surface of the light-emitting element to reduce the areaof the light-emitting surface correspondingly.

The luminance changes gradually between the outer and inner sides of theside (i.e., one side of the light-emitting surface of the light-emittingdevice) on which the side of the light-transmissive member is locatedinside the side of the light-emitting surface of the light-emittingelement, but the effects on the clearness of the cut-off line are small.

The light-emitting device according to this embodiment is described indetail below, with reference to the drawings.

FIG. 1 is a schematic perspective view of the light-emitting deviceaccording to one embodiment of the present invention. FIG. 2 is aschematic plan view of the light-emitting device according to theembodiment. FIG. 3 is a schematic cross-sectional view taken along theline A-A in FIG. 2 . FIG. 4 is a schematic cross-sectional view takenalong the line B-B in FIG. 2 .

A light-emitting device 100 according to this embodiment includes

-   -   (a) a substrate 10,    -   (b) light-emitting elements 1 on or above the substrate 10,    -   (c) a plate-shaped light-transmissive member 7 having a lower        surface that faces the upper surfaces serving as the        light-emitting surfaces of the light-emitting elements 1, and    -   (d) a covering member 5 covering lateral surfaces of the        light-emitting elements 1 and lateral surfaces of the        light-transmissive member 7.

The light-emitting elements 1 are, for example, flip-chip mounted on orabove the substrate 10 with electrically-conductive bonding members 20therebetween as shown in FIG. 3 and FIG. 4 . Although the light-emittingelements 1 are simplified in FIG. 3 and FIG. 4 , each of thelight-emitting elements 1 includes, for example, a p-side electrode andan n-side electrode on the same surface, and the p-side electrode andthe n-side electrode are respectively connected to a first electrode 11and a second electrode 12 disposed on the substrate 10 via theelectrically-conductive bonding members 20. As described below indetail, the light-transmissive member 7 is bonded to the light-emittingsurfaces of the light-emitting elements 1 with a light-guiding member 40therebetween. The light-transmissive member 7 contains a phosphor 8 thatis excited by light emitted from the light-emitting elements 1 and emitslight with a wavelength longer than the wavelength of the light emittedfrom the light-emitting elements 1.

The covering member 5 is, for example, a reflective member containing awhite pigment mixed in a matrix made of resin or the like and coverslateral surfaces of the light-emitting elements 1, lateral surfaces ofthe light-guiding member 40, and lateral surfaces of thelight-transmissive member 7, on the substrate 10. The covering member 5covers the lateral surfaces to encircle the entire peripheries of thelight-emitting elements 1, the light-guiding member 40, and thelight-transmissive member 7. An upper surface 7 s (in other words, thelight-emitting surface of the light-emitting device 100) of thelight-transmissive member 7 is substantially flush with the uppersurface of the covering member 5. The light-emitting device 100 havingthe above structure has high upward light extraction efficiency becauselight laterally emitted from the light-emitting elements 1 and thelight-transmissive member 7 is reflected off the covering member 5 andemitted upward.

In particular, in the light-emitting device 100, the light-transmissivemember 7 is out of alignment with the light-emitting elements 1 as canbe seen from FIG. 2 and FIG. 4 . If the light-emitting device 100 havingthe above structure is used as a light source module for a headlight, aheadlight having a clear cut-off line in its light distribution patternis provided using a simple and small optical system.

<Arrangement of Light-Emitting Elements 1 and Light-Transmissive Member7>

The upper surfaces of the light-emitting elements 1 each have arectangular shape having a first lateral side 1 a and a second lateralside 1 b that are opposite to each other, and a third lateral side 1 cand a fourth lateral side 1 d that are opposite to each other as shownin FIG. 2 . The upper surface 7 s of the light-transmissive member 7 hasa rectangular shape having a fifth side 7 a (i.e., a first lateral sideof the upper surface 7 s of the light-transmissive member) and a sixthside 7 b (i.e., a second lateral side of the upper surface 7 s of thelight-transmissive member) that are opposite to each other, and aseventh side 7 c (i.e., a third lateral side of the upper surface 7 s ofthe light-transmissive member) and an eighth side 7 d (i.e., a fourthlateral side of the upper surface 7 s of the light-transmissive member)that are opposite to each other.

The light-transmissive member 7 is disposed on or above thelight-emitting elements 1 such that the fifth side 7 a is locatedoutside the first sides 1 a and such that the sixth side 7 b is locatedinside the second sides 1 b in a plan view from above as shown in FIG. 2. The light-emitting device according to this embodiment includes aplurality of light-emitting elements 1 as shown in FIG. 2 and otherdrawings, and the light-transmissive member 7 is disposed on or abovethe two light-emitting elements 1 such that the fifth side 7 a of thelight-transmissive member 7 is located outside the first sides 1 a ofthe two light-emitting elements 1 and such that the sixth side 7 b islocated inside the second sides 1 b of the two light-emitting elements 1as shown in FIG. 2 .

In the case where the light-emitting device 100 according to the presentembodiment includes a plurality of light-emitting elements 1 each havingthe first to fourth sides 1 a to 1 d, it is preferable that the firstsides 1 a of the light-emitting elements 1 lie on the same straight line(first straight line). In addition, it is more preferable to arrange thelight-emitting elements 1 on or above the substrate 10 such that thefirst sides 1 a lie on the first straight line and such that the secondsides 1 b lie on a second straight line parallel to the first straightline.

In addition, it is preferable that the upper surface 7 s of thelight-transmissive member 7 be substantially flat and substantiallyparallel to the lower surface of the light-transmissive member 7. Amongthe lateral surfaces continuous with the upper surface 7 s of thelight-transmissive member 7, the lateral surface continuous with theupper surface 7 s via the fifth side 7 a is preferably continuous withthe lower surface and substantially perpendicular to the upper surface 7s.

In the light-emitting device 100 according to the embodiment describedabove, the light-transmissive member 7 is disposed such that the fifthside 7 a of the light-transmissive member 7 is located outside the firstsides 1 a of the light-emitting elements 1 in a plan view from above.Hence, the luminance changes abruptly between the outer and inner sidesof the boundary corresponding to the fifth side 7 a of thelight-transmissive member 7 between the light-emitting surface and thecovering member 5 (left-hand rising edge of the relative luminance inthe graph of FIG. 5 ). A headlight that offers a clear cut-off lineusing a simple optical system can therefore be provided when thelight-emitting device 100 is used as a light source for a headlight.

Because the light-transmissive member 7 is disposed on or above thelight-emitting elements 1 such that the sixth side 7 b of thelight-transmissive member 7 is located inside the second sides 1 b ofthe light-emitting elements 1 in a plan view from above in thelight-emitting device 100 according to this embodiment, the width of theupper surface 7 s of the light-transmissive member 7 is narrowed down;in other words, the width of the light-emitting surface of thelight-emitting device 100 is narrowed down. In short, the area of thelight-emitting surface is reduced. Accordingly, the optical system canbe miniaturized when the light-emitting device 100 is used as a lightsource for a headlight. If the light-transmissive member 7 is disposedon or above the light-emitting elements 1 such that the sixth side 7 bof the light-transmissive member 7 is located inside the second sides 1b of the light-emitting elements 1, the luminance changes graduallybetween the outer and inner sides of the boundary corresponding to thesixth side 7 b of the light-transmissive member 7 between thelight-emitting surface and the covering member 5 (right-hand rising edgeof the relative luminance in the graph of FIG. 5 ). However, because thelight-transmissive member 7 is disposed such that the fifth side 7 a ofthe light-transmissive member 7 is located outside the first sides 1 aof the light-emitting elements 1 in a plan view from above in thelight-emitting device 100 according to this embodiment, the structure inwhich the sixth side 7 b of the light-transmissive member 7 is locatedinside the second sides 1 b of the light-emitting elements 1 has smalleffects on the clearness of the cut-off line. The graph of the relativeluminance of FIG. 5 shows an example of the relative luminance in thecross section taken along the line B-B in FIG. 2 .

As described above, if the light-emitting device 100 according to thisembodiment is used as a light source for a headlight, a headlight thatoffers a clear cut-off line using a simple and small optical system canbe made.

In the embodiment of the light-emitting device described above, thelight-transmissive member 7 is disposed such that the seventh side 7 cand the eighth side 7 d of the light-transmissive member 7 arerespectively located outside the third side 1 c and the fourth side 1 dof the light-emitting elements 1. The luminance therefore changesabruptly between the outer and inner sides of the seventh side 7 c andthe eighth side 7 d, so that a headlight that offers a clear cut-offline using a simpler optical system can be provided when thelight-emitting device 100 is used as a light source for a headlight.

In the light-emitting device according to this embodiment, thelight-transmissive member 7 may be disposed on or above thelight-emitting elements 1 such that the seventh side 7 c and the eighthside 7 d are respectively located inside the third side 1 c and thefourth side 1 d. This structure further reduces the area of thelight-emitting surface of the light-emitting device 100, and the opticalsystem can be further miniaturized when the light-emitting device 100 isused as a light source for a headlight.

In the light-emitting device according to this embodiment, thelight-transmissive member 7 may be disposed on or above thelight-emitting elements such that the seventh side 7 c is located insidethe third side 1 c and such that the eighth side 7 d is located outsidethe fourth side 1 d.

In the light-emitting device according to the above embodiment, onelight-transmissive member 7 covers a plurality of light-emittingelements 1.

However, the light-emitting device according to this embodiment is notexclusively limited to this structure, and one light-transmissive member7 may cover one light-emitting element 1. Alternatively, a plurality oflight-transmissive members 7 each covering one or two or morelight-emitting elements 1 may be disposed as in modifications describedlater.

In the light-emitting device according to the above embodiment, thelight-transmissive member 7 is disposed on or above the light-emittingelements 1 such that the fifth side 7 a is located outside the firstsides 1 a and such that the sixth side 7 b is located inside the secondsides 1 b in a plan view from above.

However, the light-emitting device according to this embodiment is notexclusively limited to this structure, and the light-transmissive member7 may be disposed on or above the light-emitting elements 1 such thatthe fifth side 7 a overlaps the first sides 1 a and such that the sixthside 7 b is located inside the second sides 1 b in a plan view fromabove.

The light-emitting device according to the above embodiment includes thelight-transmissive member 7 containing the phosphor 8.

However, the light-emitting device according to this embodiment is notlimited to this structure, and a light-transmissive member 7 containingno phosphor may be included.

First Modification

FIG. 6 is a schematic plan view of a light-emitting device according toa first modification.

The light-emitting device according to the first modification issubstantially the same as the light-emitting device according to thisembodiment shown in FIG. 2 and other drawings except that fourlight-emitting elements 1 are used.

The light-emitting device according to the first modification having theabove structure has substantially the same effects as the light-emittingdevice according to this embodiment and can provide higher luminancethan the luminance of the light-emitting device shown in FIG. 2 andother drawings.

Second Modification

FIG. 7 is a schematic plan view of a light-emitting device according toa second modification. FIG. 8 is a schematic cross-sectional view of thelight-emitting device according to the second modification taken alongthe line C-C in FIG. 7 .

The light-emitting device according to the second modification issubstantially the same as the light-emitting device according to thefirst modification except that the shape of the light-transmissivemember 7 differs from the shape in the light-emitting device accordingto the first modification. In the light-emitting device according to thesecond modification, the light-transmissive member 7 has a second uppersurface located outside and below the upper surface 7 s (hereinafterreferred to as a first upper surface) of the light-transmissive member 7in the second modification, and the second upper surface is covered withthe covering member 5. The following specifically describes differencesfrom the embodiment described above and the first modification.

In the light-emitting device according to the second modification, thelight-transmissive member 7 has the lower surface bonded to thelight-emitting elements 1 and the upper surfaces opposite to the lowersurface. A substantially flat lower surface constitutes the lowersurface of the light-transmissive member 7, and the upper surfacesinclude at least two upper surfaces: a first upper surface 7 s 1 and asecond upper surface 7 s 2. There is a difference in level between thefirst upper surface 7 s 1 and the second upper surface 7 s 2.Specifically, the thickness of the light-transmissive member 7 betweenthe second upper surface 7 s 2 and the lower surface thereof is smallerthan the thickness of the light-transmissive member 7 between the firstupper surface 7 s 1 and the lower surface thereof.

In the light-emitting device according to the second modification, thefirst upper surface 7 s 1 of the light-transmissive member 7 has thefifth side 7 a and a sixth internal side 7 b 1 opposite to the fifthside 7 a. The second upper surface 7 s 2 of the light-transmissivemember 7 has a sixth external side 7 b 2 located outside the sixthinternal side 7 b 1. In other words, the light-transmissive member 7 hasthe second upper surface 7 s 2 located outside the sixth internal side 7b 1 in a plan view from above.

In the light-emitting device according to the second modification, thelight-transmissive member 7 is disposed on or above the light-emittingelements 1 such that (a) the fifth side 7 a is located outside the firstsides 1 a of the light-emitting elements 1, (b) the sixth internal side7 b 1 is located inside the second sides 1 b of the light-emittingelements 1, and (c) the sixth external side 7 b 2 is located outside thesecond sides 1 b of the light-emitting elements 1 in a plan view fromabove as shown in FIG. 7 and FIG. 8 .

In this case, the first upper surface 7 s 1 of the light-transmissivemember 7 is preferably a substantially flat surface substantiallyparallel to the lower surface, and among the lateral surfaces continuouswith the first upper surface 7 s 1 of the light-transmissive member 7,at least the lateral surface continuous with the first upper surface 7 s1 via the fifth side 7 a is preferably continuous with the lower surfaceand substantially perpendicular to the first upper surface 7 s 1. Thesecond upper surface 7 s 2 may be substantially parallel to the lowersurface or may be inclined relative to the lower surface.

In the light-emitting device according to the second modification, thecovering member 5 covers the second upper surface 7 s 2 such that thefirst upper surface 7 s 1 is exposed. With this structure, the firstupper surface 7 s 1 of the light-transmissive member 7 serves as thelight-emitting surface of the light-emitting device.

In the light-emitting device according to the second modification havingthe above structure, the light-transmissive member 7 is disposed suchthat the fifth side 7 a of the light-transmissive member 7 is locatedoutside the first sides 1 a of the light-emitting elements 1 in a planview from above. Hence, the luminance changes abruptly between the outerand inner sides of the boundary corresponding to the fifth side 7 a ofthe light-transmissive member 7 between the light-emitting surface andthe covering member 5. A headlight that offers a clear cut-off lineusing a simple optical system can therefore be provided when thelight-emitting device according to the second modification is used as alight source for a headlight.

Because the light-transmissive member 7 is disposed on or above thelight-emitting elements 1 such that the sixth internal side 7 b 1 of thelight-transmissive member 7 is located inside the second sides 1 b ofthe light-emitting elements 1 in a plan view from above in thelight-emitting device according to the second modification, the width ofthe first upper surface 7 s 1 of the light-transmissive member 7 isnarrowed down; in other words, the width of the light-emitting surfaceof the light-emitting device is narrowed down, thereby reducing the areaof the light-emitting surface. Accordingly, the optical system can beminiaturized when the light-emitting device 100 is used as a lightsource for a headlight.

In the case where the light-transmissive member 7 in the light-emittingdevice according to the second modification contains a phosphor; inother words, in the case where a desired emission color of thelight-emitting device is obtained because the emitted light containslight having undergone wavelength conversion by the phosphor, the lowersurface of the light-transmissive member 7 covering the entirelight-emitting surfaces of the light-emitting elements 1 prevents lightemitted from the light-emitting elements from bypassing thelight-transmissive member 7 and leaking out.

Third Modification

FIG. 9 is a schematic plan view of a light-emitting device according toa third modification.

The light-emitting device according to the third modification differsfrom the light-emitting device according to the embodiment describedabove in that three light-emitting elements 1 and two light-transmissivemembers 7 are included.

In the light-emitting device according to the third modification, onelight-transmissive member 7 is disposed on or above two light-emittingelements 1, and the other light-transmissive member 7 is disposed on orabove one light-emitting element 1. Specifically, one of the twolight-transmissive members 7 is disposed over two light-emittingelements 1 such that the fifth side 7 a is located outside the firstsides 1 a of the two light-emitting elements 1 and such that the sixthside 7 b is located inside the second sides 1 b of the twolight-emitting elements 1 in a plan view from above as shown in FIG. 9 .

The other one of the two light-transmissive members 7 is disposed on orabove the other light-emitting element 1 such that the fifth side 7 a islocated outside the first side 1 a of the light-emitting element 1 andsuch that the sixth side 7 b is located inside the second side 1 b ofthe light-emitting element 1 in a plan view from above as shown in FIG.9 .

In the above case where the light-emitting device includes a pluralityof light-emitting elements 1, combinations of the numbers, intervals,and densities of the light-transmissive members 7 and the light-emittingelements 1 can be selected to provide a light source suitable for adesired light distribution pattern.

In the light-emitting device according to the third modification, thetwo light-transmissive members 7 are disposed such that the seventhsides 7 c and the eighth sides 7 d of the light-transmissive members 7are respectively located outside the third sides 1 c and the fourthsides 1 d of the light-emitting elements 1.

With the light-emitting device according to the third modificationhaving the above structure, a headlight that offers a clear cut-off linein the light distribution pattern using a simpler optical system can beprovided when the light-emitting device 100 is used as a light sourcefor a headlight.

Because the light-emitting device according to the third modificationcan have a more reduced area of the light-emitting surface, the opticalsystem can be further miniaturized when the light-emitting deviceaccording to the third modification is used as a light source for aheadlight.

Fourth Modification

FIG. 10 is a schematic plan view of a light-emitting device according toa fourth modification.

The light-emitting device according to the fourth modification issubstantially the same as the light-emitting device according to thethird modification except that the two light-transmissive members 7 inthe light-emitting device according to the third modification arechanged such that the seventh sides 7 c and the eighth sides 7 d of thelight-transmissive members 7 are respectively located inside the thirdsides 1 c and the fourth sides 1 d of the light-emitting elements 1.

Because the area of the light-emitting surface of the light-emittingdevice according to the fourth modification having the above structurecan be smaller than in the light-emitting device according to the thirdmodification, the optical system can be further miniaturized when thelight-emitting device according to the fourth modification is used as alight source for a headlight.

Fifth Modification

FIG. 11 is a schematic plan view of a light-emitting device according toa fifth modification.

The light-emitting device according to the fifth modification issubstantially the same as the light-emitting device according to thefourth modification except that the shapes of the two light-transmissivemembers 7 differ from the shapes in the light-emitting device accordingto the fourth modification.

Specifically, in the light-emitting device according to the fifthmodification, the light-transmissive members 7 each have the secondupper surface 7 s 2 located outside and below the upper surface (firstupper surface 7 s 1) of the light-transmissive members 7 in the fourthmodification, and the second upper surface 7 s 2 is covered with thecovering member 5. The second upper surface 7 s 2 of eachlight-transmissive member 7 in the light-emitting device according tothe fifth modification is disposed on the three sides other than thefifth side 7 a in a plan view from above. In the light-emitting deviceaccording to the fifth modification, the light-transmissive members 7have substantially flat lower surfaces bonded to the light-emittingelements 1.

In the light-emitting device according to the fifth modification, thepositional relation between the first upper surfaces 7 s 1 of thelight-transmissive members 7 and the light-emitting elements 1 issubstantially the same as the positional relation between the uppersurfaces 7 s of the light-transmissive members 7 and the light-emittingelements 1 in the light-emitting device according to the fourthmodification in a plan view from above. The light-transmissive members 7are disposed on or above the light-emitting elements 1 such that theirlower surfaces are located outside the peripheries of the correspondinglight-emitting elements 1.

A headlight that offers a clear cut-off line using a simpler opticalsystem can be provided when the light-emitting device according to thefifth modification having the above structure is used as a light sourcefor a headlight.

Because the light-emitting device according to the fifth modificationcan have a reduced area of the light-emitting surface, a light-emittingdevice with a high luminance can be provided. In addition, the opticalsystem can be further miniaturized when the light-emitting device isused as a light source for a headlight.

The light-emitting device according to the fifth modification having theabove structure has substantially the same effects as the light-emittingdevice according to the fourth modification. Furthermore, in the casewhere the light-transmissive members 7 contain a phosphor, the phosphor8 can be efficiently irradiated with light emitted from thelight-emitting elements 1 because the light-transmissive members 7 coverthe entire light-emitting surfaces of the light-emitting elements 1.

Sixth Modification

FIG. 12 is a schematic plan view of a light-emitting device according toa sixth modification.

In the light-emitting device according to the sixth modification, thelight-transmissive member 7 has the second upper surface 7 s 2 locatedoutside and below the upper surface 7 s 1, and the second upper surface7 s 2 is covered with the covering member 5. The light-transmissivemember 7 is disposed on or above the light-emitting element 1 such thatthe fifth side 7 a is located outside the first side 1 a of thelight-emitting element 1 and such that the sixth internal side 7 b 1 andthe sixth external side 7 b 2 are both located inside the second side 1b of the light-emitting element 1 in a plan view from above as shown inFIG. 12 . In the light-emitting device according to the sixthmodification, the seventh side 7 c and the eighth side 7 d of thelight-transmissive member 7 are located outside the third side 1 c andthe fourth side 1 d of the light-emitting element 1.

A headlight that offers a clear cut-off line using a simpler opticalsystem can be provided when the light-emitting device according to thesixth modification having the above structure is used as a light sourcefor a headlight.

Because the light-emitting device according to the sixth modificationcan have a more reduced area of the light-emitting surface, the opticalsystem can be further miniaturized when the light-emitting device isused as a light source for a headlight.

The following describes the members and structure of each of thelight-emitting devices according to the present embodiment andmodifications.

(Substrate 10)

The substrate 10 is a member on or above which the light-emittingelement is arranged, and includes wiring that electrically connects theelectrodes of the light-emitting element and external electrodes. Apreferable main material for the substrate 10 is an insulating materialthat transmits less extraneous light and less light emitted from thelight-emitting element. Examples of the material include ceramics, suchas alumina and aluminum nitride, and resins, such as phenolic resins,epoxy resins, polyimide resins, bismaleimide triazine resins, andpolyphthalamide. In the case where a resin is used, an inorganic filler,such as glass fiber, silicon oxide, titanium oxide, and alumina, may bemixed with the resin as appropriate. Such a filler can improve themechanical strength, reduce the thermal expansion coefficient, andimprove the light reflectance. The substrate 10 may be a metal member onthe surface of which an insulating material is formed. The wiring isformed into a predetermined pattern on the insulating material. Thematerial for the wiring can be at least one selected from gold, silver,copper, and aluminum. The wiring can be formed by plating, vaporevaporation, sputtering, or the like.

(Light-Emitting Element 1)

A light emitting diode is preferably used as the light-emitting element1. The light-emitting element can be appropriately selected to exhibitan appropriate emission wavelength. Examples of a blue or greenlight-emitting element include a light-emitting element that includesZnSe, a nitride semiconductor (In_(X)Al_(Y)Ga_(1-X-Y)N, where 0≤X, 0≤Y,and X+Y≤1) or GaP. For a red light-emitting element, GaAlAs, AlInGaP, orthe like can be used. Semiconductor light-emitting elements made ofother materials can also be used. The compositions, emission colors,sizes, and number of the light-emitting elements to be used can beselected appropriately depending on the purpose. In the case where thelight-emitting device contains a phosphor, for example, a nitridesemiconductor (In_(X)Al_(Y)Ga_(1-X-Y)N, where 0≤X, 0≤Y, and X+Y≤1) issuitable because it can emit light with short wavelengths that canefficiently excite the phosphor. The emission wavelength can be selectedby changing the materials for the semiconductor layers and their mixingratios.

The light-emitting element in this embodiment includes positive andnegative electrodes on the same surface and is flip-chip mounted on orabove the substrate by bonding the positive and negative electrodes tothe substrate using electrically-conductive bonding members. The uppersurface of the light-emitting element opposite to the lower surface onwhich the electrodes are formed serves as the main emission surface.Because such a light-emitting element is connected to the substrateusing electrically-conductive bonding members, such as bumps andelectrically-conductive pastes, the area of contact between theelectrodes and the substrate can be larger than in the case of alight-emitting element that is connected using metal wires or the like,and the contact resistance can be reduced.

The light-emitting element is formed by, for example, layering a nitridesemiconductor layer on a light-transmissive sapphire growth substrate.The sapphire substrate is located at the upper surface of thelight-emitting element 1 and constitutes the main emission surface. Thegrowth substrate may be removed by, for example, abrasion or laser liftoff (LLO).

(Light-Transmissive Member 7)

The light-transmissive member 7 can transmit light emitted from thelight-emitting element 1 and allows the light to exit to the outside.The light-transmissive member 7 may contain a light-diffusing materialand a phosphor that can perform wavelength conversion of at least partof incident light. The light-transmissive member 7 can be made of, forexample, resin, glass, or an inorganic substance. Examples of thelight-transmissive member containing a phosphor include sintered bodiesof phosphors, and mixtures of phosphors and substances such as resin,glass, ceramics, and other inorganic substances. Alternatively, a moldor compact of resin, glass, or a ceramic on the surface of which a resinlayer containing a phosphor is formed can be used. The thickness of thelight-transmissive member 7 is, for example, about 50 μm to 300 μm.

The light-transmissive member 7 can be bonded to the light-emittingelement using, for example, the light-guiding member described later.The light-transmissive member can be directly bonded to thelight-emitting element by compression, sintering, surface-activatedbonding, atomic diffusion bonding, or hydroxy-group bonding.

(Phosphor)

For the phosphor that can be contained in the light-transmissive member7, a phosphor that can be excited by light emitted from thelight-emitting element is used. Examples of a phosphor that can beexcited by a blue or ultraviolet light-emitting element includecerium-activated yttrium-aluminum-garnet phosphors (Ce:YAG);cerium-activated lutetium-aluminum-garnet phosphors (Ce:LAG); europium-and/or chromium-activated nitrogen-containing calcium aluminosilicatephosphors (CaO—Al₂O₃—SiO₂); europium-activated silicate phosphors((Sr,Ba)₂SiO₄); nitride phosphors such as β-SiAlON phosphors, CASNphosphors, and SCASN phosphors; KSF phosphors (K₂SiF₆:Mn); sulfidephosphors; and quantum-dot phosphors. Combinations of such phosphors andblue or ultraviolet light-emitting elements enable light-emittingdevices emitting various colors (such as white light-emitting devices)to be manufactured.

(Covering Member 5)

The covering member 5 covers the lateral surfaces of the light-emittingelement 1 and the light-transmissive member 7. The covering member 5 canbe formed using, for example, a light-reflective material having a highlight reflectance. Specifically, a light-reflective material having areflectance of light emitted from the light-emitting element of 60% ormore, more preferably 80% or 90% or more can be used for the coveringmember 5. The light-reflective material includes, for example, a resinmaterial containing a light-reflective substance.

Examples of the resin serving as the matrix constituting the coveringmember 5 include silicone resins, modified silicone resins, epoxyresins, modified epoxy resins, acrylic resins, and hybrid resins eachcontaining at least one of these resins. The covering member 5 can beformed by mixing a reflective substance in the resin matrix. Examples ofthe light-reflective substance include oxides containing any of Ti, Zr,Nb, Al, and Si; AlN; and MgF. Titanium dioxide (TiO2) is preferable. Itis preferable that particles having a refractive index different fromthe refractive index of the matrix resin be dispersed as thelight-reflective substance in the matrix resin. Because the amounts ofreflection and transmission of light vary depending on the concentrationand density of the light-reflective substance, the concentration anddensity can be appropriately adjusted depending on the shape and size ofthe light-emitting device.

(Light-Guiding Member 40)

The light-emitting device may include the light-guiding member 40 thatcovers at least a portion of the lateral surfaces of the light-emittingelement 1. In the case where part of the upper surface of thelight-emitting element 1 is exposed out of the light-transmissive member7, the light-guiding member 40 preferably covers the part of the uppersurface of the light-emitting element exposed out of thelight-transmissive member 7. In addition, the light-guiding member 40preferably covers the part of the lower surface of thelight-transmissive member 7 exposed out of the light-emitting element 1.The light-guiding member 40 may be disposed also between thelight-emitting element and the light-transmissive member 7 to functionas an adhesive member for bonding the light-emitting element to thelight-transmissive member 7. If this light-guiding member 40 isincluded, the outer surfaces of the light-guiding member 40 reflectlight emitted from the upper and lateral surfaces of the light-emittingelement 1 to guide the reflected light to the light-transmissive member7.

The light-guiding member 40 is preferably made of a resin materialbecause resin materials are easy to handle and process. A resin materialmade of a resin or hybrid resin containing at least one of siliconeresins, modified silicone resins, epoxy resins, modified epoxy resins,acrylic resins, and fluorocarbon resins can be used. The light-guidingmember 40 can be formed by utilizing the viscosity of the resin materialfor the light-guiding member 40 and the wettability of thelight-emitting element 1 by the resin material.

The light-emitting device may optionally include other elements andelectronic components such as a protective element. These elements andelectronic components are preferably embedded in the covering member 5.

What is claimed is:
 1. A light-emitting device comprising: a substrate;at least one light-emitting element on or above the substrate, the atleast one light-emitting element having a rectangular shape in a planview from above the light-emitting device and having an upper surfaceserving as a light-emitting surface of the at least one light-emittingelement; a plate-shaped light-transmissive member having a rectangularshape in a plan view from above the light-emitting device and having alower surface that faces the upper surface of the at least onelight-emitting element; a covering member that covers a lateral surfaceof the at least one light-emitting element and a lateral surface of thelight-transmissive member; and a light-guiding member that is disposedbetween the light-emitting element and the light-transmissive member,wherein the upper surface of the at least one light-emitting elementwith the rectangular shape has a first lateral side and a second lateralside opposite to each other, and a third lateral side and a fourthlateral side opposite to each other, wherein an upper surface of thelight-transmissive member with the rectangular shape has a first lateralside and a second lateral side opposite to each other, and a thirdlateral side and a fourth lateral side opposite to each other, whereinthe light-transmissive member is disposed on or above the at least onelight-emitting element such that, in a plan view from above thelight-emitting device: the first lateral side of the upper surface ofthe light-transmissive member is outside the first lateral side of theupper surface of the at least one light-emitting element, and nolight-emitting element in the light emitting device overlaps the firstlateral side of the upper surface of the light-transmissive member, andthe second lateral side of the upper surface of the light-transmissivemember is inside the second lateral side of the upper surface of the atleast one light-emitting element, and wherein the light-guiding memberis disposed at the lateral surface of the at least one light-emittingelement on the first lateral side of the upper surface of the at leastone light-emitting element, and the covering member is disposed at thelateral surface of the at least one light-emitting element on the secondlateral side of the upper surface of the at least one light-emittingelement.
 2. The light-emitting device according to claim 1, wherein aregion not having the light-guiding member is provided on the uppersurface of the at least one light-emitting element.
 3. Thelight-emitting device according to claim 1, wherein a distance betweenthe first lateral side of the light-transmissive member and a lateralsurface of the covering member is the same as a distance between thesecond lateral side of the light-transmissive member and a lateralsurface of the covering member.
 4. The light-emitting device accordingto claim 1, wherein a distance between the first lateral side of the atleast one light-emitting element and a lateral surface of the coveringmember is larger than a distance between the second lateral side of theat least one light-emitting element and a lateral surface of thecovering member.